Method of making bearings



Dec. 7, 1965 J. c. GoULD ETAL 3,221,392

METHOD OF MAKING BEARINGS Original Filed Sept. 28, 1960 YNE/s( UnitedStates Patent O 3,221,392 METHGD F MAKING BEARINGS .lames C. Gould andVictor Gallatin, Ann Arbor, Mich.,

assignors to Federal-Mogul-Bower Bearings, Inc., Detroit, Mich., acorporation of Michigan @riginal application Sept. 28, 1960, Ser. No.59,086. Di-

vided and this application July 30, 1964, Ser. No. 392,982

6 Claims. (Cl. 29--149.5)

This application is a division of co-pending application, Serial No.59,086, filed September 28, 1960, by James C. Gould and Victor Gallatinfor Method of Making Bearings, now abandoned.

The present invention broadly pertains to bearings, and moreparticularly to an improved composite bearing and method of making samecomprising an aluminum-lead alloy bearing surface tenaciously bonded toa hard metal backing strip.

Composite bearings of the general type to which the present invention isapplicable utilize a strong, hard metal backing strip to one surface ofwhich a thin bearing surface layer is tenaciously bonded. Bearing layershave alternatively been applied to the hard metal backing strip byapplying and bonding a thin sheet of the bearing metal to the surface ofthe hard metal backing member or by employing powder metallurgicaltechniques wherein a powder blend of bearing metals is applied to andsintered on the surface of the hard metal backing member becoming firmlybonded thereto. It is the function of the hard metal backing strip tosupport the bearing surface layer thereon and prevent excessivedeformation thereof when subjected to high bearing loads during use.

A variety of metals such as copper and aluminum for example, haveheretofore been employed in combination with one or more of theso-called lubricity metals such as for example, lead, tin, cadmium, andthe like, to form a bearing surface layer which is tenaciously bonded tothe hard metal backing strip. Of the foregoing metals, aluminum-leadalloys have been found particularly satisfactory for providing bearingsurface layers which will withstand high loads, minimize the wear ofunhardened shafts, and which have satisfactory fatigue characteristics.The extensive use of aluminum-lead alloys in composite bearings of thegeneral type herein described has heretofore been limited due to theinability of alloying lead with aluminum in appreciable quantities. Forexample, the low miscibility of lead in molten aluminum restricts thequantity of lead therein to a level of only about 0.2%. The problem ofproviding aluminum-lead alloys containing greater quantities of leadtherein was partly surmounted by resorting to powder metallurgicaltechniques for applying an aluminum-lead bearing surface layer to a hardmetal backing strip. A method for achieving an aluminum-lead alloycontaining a quantity of lead in an amount above the 0.2% limitation isdisclosed in United States Patent No. 2,815,567 issued December 10, 1957and assigned to the same assignee as the present invention. Inaccordance with the teachings of the aforementioned patent,aluminum-lead alloy surface layers containing up to about lead can bemanufactured by preheating in a non-oxidizing atmosphere a powder blendcomprising aluminum, or aluminum alloy powder and lead powder on thesurface of a hard metal backing strip and thereafter compacting thebearing surface layer ICC and tenaciously bonding the compacted layer tothe backing strip. However, the quantity of lead which could be alloyedwith the aluminum by the method disclosed in the patent was limited to alevel of about 15% because of the excessive exudation of molten leadfrom the bearing surface layer during the hot compacting thereof.

Accordingly, it is a primary object of the present invention to providea unique aluminum-lead alloy and method of making same which contains aconcentration of lead substantially in excess of that heretoforeobtainable.

Another object of the present invention is to provide an improved methodfor applying and tenaciously bonding an aluminum-lead alloy layer to thesurface of a hard metal backing member and which aluminum-lead alloycontains a concentration of lead ranging upwards to a level of aboutStill another object of the present invention is to provide an improvedaluminum-lead alloy composite bearing and method of making same andwhich bearing is characterized by its high strength, excellentdurability over a wide range of operating conditions, and which is ofeconomical manufacture.

Other objects and advantages of the present invention will becomeapparent from the following detailed description taken in conjunctionwith the accompanying drawings, wherein:

FIGURE 1 is a diagrammatic view illustrating an apparatus for applyingthe aluminum-lead alloy bearing layer to the surface of a hard metalbacking strip in accordance with the preferred practice of the presentinvention, and

FIGURE 2 is a fragmentary magnified View of the hot rolling compactingstep of the composite bearing strip shown in FIGURE 1.

The novel aluminum-lead alloy and composite bearing produced therefromare obtained through the surprising and unexpected discovery that byblending aluminum and lead monoxide powders in the appropriateproportions and thereafter preheating the blended powder at an elevatedtemperature in a reducing atmosphere the resultant preheated powderlayer can be densied by hot rolling without incurring an appreciableloss of lead by exudation. The foregoing discovery has enabled thesuccessful production of aluminum lead alloys containing up to about 70%lead and which alloy can be readily bonded in the form of a thin layerto the surface of a hard metal backing strip. It will be understood thatthe method herein described is also applicable to the manufacture ofaluminum-lead alloys and composite bearing strips having lower leadcontents with the range heretofore obtainable by the method disclosed inthe aforementioned patent. The resultant aluminum-lead alloy produced ischaracterized as a densely compacted mass wherein the lead is finelydistributed throughout the aluminum matrix and which includes a minorportion of unreduced lead monoxide ranging up to about 5% of themetallic lead constituent.

It will be understood that the compositions of the aluminum-lead bearingalloys as described in this specification and in the subjoined claims isexpressed, unless otherwise noted, in terms of percentages by weight.

The composition of the aluminum-lead alloy produced is established bythe relative proportions of powdered aluminum and lead monoxide (PbO)powder used in preparing the powder blend prior to processing. Thealuminum powders which can satisfactorily be used in the practice of thepresent invention, include not only pure aluminum but conventionalprealloyed aluminum powders containing other metals and/or elements suchas, for example, silicon, copper, nickel, magnesium and the like. Theuse of prealloyed aluminum powders in lieu of a pure aluminum powder isgenerally desirable in order to impart the desired strength andtoughness to the aluminum matrix to enable it to withstand high loadingsuch as may be encountered in heavy duty operation. Two prealloyedaluminum powders which have been found to be eminently satisfactoryinclude an alloy consisting essenstially of 96% aluminum and 4% siliconand an aluminum alloy consisting essentially of 98% aluminum, 1% nickeland 1% copper.

The particle size of the aluminum powder, regardless of whether itconsists of a pure aluminum or prealloyed aluminum powder should besufficiently small to facilitate obtaining a relatively uniform powderblend with the lead monoxide and moreover, to provide for a resultantalloy having a relatively line grain structure. Particles sizes rangingfrom about less than 100 mesh to about less than 325 mesh, andpreferably less than 100 mesh with from about 40% to 50% thereof lessthan 325 mesh can be satisfactorily employed.

The lead content of the aluminum-lead alloy is introduced in the form offinely particulated lead monoxide (PbO) or litharge, which ispreliminairly blended with the aluminum powder prior to processing. Thelead monoxide or lithrage can range in particle size within the range ofparticle sizes specified above for the aluminum powders, and preferablyis of a finer particle size facilitating uniform distribution during theblending operation and a tine distribution of lead in the resultantalloy. Of the variety of lead monoxide powders available, theconventional so-called Mill-Run litharge has provided excellent resultswhen combined with varying proportions of aluminum powders. The nominalchemical analysis and particle size of a Mill-Run litharge utilized inthe preparation of the aluminum lead alloys and composite bearingscomprising the present invention is tabulated below:

M ill-Run ltharge analysis Nominal chemical analysis:

PbO more than 99.5% by wt. Total HcZHaOz insol 0.25% maximum. True Pb3040.10% maximum. Free Pb 0.05 maximum. Particle size:

Average particle size 5 microns. Retained on 325 mesh screen Less than1.0%.

Appropriate proportions of the aluminum and lead monoxide powders arepreliminarily blended in a suitable vessel provided with agitation suchas, for example, a ball or pebble mill, until a substantiallyhomogeneous mixture is obtained. Since the lead monoxide powder issubstantially completely reduced during the preheating step in areducing atmosphere, the loss in weight thereof due to the liberation ofoxygen must be allowed for to achieve a resultant alloy having thedesired lead content. For example, to allow for the approximate 7%reduction in the weight of the lead monoxide, about 72% lead monoxidemust be blended with about 28% aluminum powder to yield a resultantalloy containing about 70% lead. The blended powdered mass is thereafterapplied to one surface of a suitable hard metal backing strip inaccordance with the apparatus diagrammatically illustrated in FIG-URE 1. As lshown in the drawing a backing strip 4 of a suitable hardmetal is unwound from a feed spool 6 and extended substantiallyhorizontally therefrom. Any one of a variety of suitable hard metals canbe satisfactorily employed for the backing strip 4 to impart the desiredstrength and toughness to the composite strip ultimately produced.Backing strips made of steel possess satisfactory strength and toughnessand enable the resultant composite strip to be subjected to furthermechanical working such as stamping or punching for example, to providea composite bearing of the desired configuration and size.

The horizontally extended backing strip 4 passes beneath a meteringaperture 8 at the base of a hopper 10 containing a substantiallyhomogeneous blend of the aluminum and lead monoxide powders. As thebacking strip 4 passes beneath the metering aperture 8 a predeterminedlayer of the powder blend 12 of the desired proportions is deposited onthe upper surface of the backing strip. The backing strip 4 with thepowder blend thereon thereafter passes under a gate or spreader 14 whichsmoothens and distributes the powder blend into a layer 16 ofsubstantially uniform thickness. After passing the spreader 14 thebacking strip 4 having the layer 16 of the powder blend 12 superposedthereon enters a preheating chamber 18 which is maintained at anelevated temperature and is provided with a reducing atmosphere. Thereducing atmosphere in the preheating chamber 18 may consist of any oneof a number of well known reducing gases, such as for example, a crackedgas atmosphere, which preferably contains a substantial percentage ofhydrogen and/or carbon monoxide which on contacting the lead monoxideparticles in the powder blend 12 causes a reduction thereof to elementallead. The reducing atmosphere also serves to prevent oxidation of thesurface of the hard metal backing strip 4 assuring a tenacious anduniform bond of the layer 16 to the backing strip.

The preheating chamber 18 is maintained at a temperature ranging fromabout 800 F. to about 1100 F. which causes a rapid reduction of the leadmonoxide to elemental molten lead which diffuses between and wets thesurfaces of the aluminum powder particles. Preheat temperatures inexcess of about 1100 F. are undesirable inasmuch as -at these highertemperatures the aluminum particles react with the ferrous backing stripforming undesirable compounds. At temperatures below about 800 F.excessive pressures must be utilized in the hot rolling and compactingstep hereinafter to be described to achieve an adequate bond between thepreheated surface layer and the hard metal backing strip. Accordingly,it is preferred that the temperatures in the preheating chamber 18 bemaintained within a range of about 800 to about 1000 F. Under thepreheating con ditions employed, the lead monoxide powder issubstantially completely reduced to metallic lead, that is, to a levelof at least about Since lead monoxide itself possesses good bearingcharacteristics and has been successfully employed as a `solid lubricantin a variety of situations, the remaining unreduced percentage of leadmonoxide in the alloy contributes to the total bearing properties of thealloy.

The backing strip 4 with the layer of the powder blend 12 thereoncontaining lead monoxide which has been substantially completely reducedin the preheating chamber 18, is passed between rotatably driven upperand lower compacting rolls 20 and 22, respectively, which exertsufficient pressure to form a relatively dense compacted layer 24 of thealuminum lead bearing alloy which is tenaciously bonded to the surfaceof the backing strip 4. During the hot compacting operation, onlyslight, if any, exudation of the molten lead occurs. This factor issurprising in view of the fact that excessive exudation occurred in themethod disclosed in the aforementioned patent limiting the amount oflead in the alloy to a level of about 15%. The reason why exudation oflead is minimized even in alloys containing up to about 70% lead byusing litharge in lieu of metallic lead is not completely understood.However, it is believed that coalescence of the minute molten leadparticles is inhibited by the unreduced lead monoxide `therein whichprevents agglomeration and resultant exudation on hot compacting.

The peripheral speed of the lower roll 22 is substantially equal to thelinear feed rate of the backing strip 4. The peripheral speed of theupper roll 20, however, in contact with the layer 16 of the powder blend12 is maintained at a speed le-ss than the linear feed rate of thebacking strip. This results in a scuing action on the hot powder blendand comprises an important feature of the method for preparing thecomposite strip. Peripheral speeds of the upper roll 20 ranging fromabout one-tenth to about one-fifth the linear speed of the backing striphaving the layer of powder blend thereon provide densely compactedbearing surface layers which are tenaciously bonded to the backing strip4 over `substantially the entire area therebetween. The lower peripheralspeed of the upper roll 20 causes the concurrent densification of thelayer 16 through a combined compacting and extrusion effect andsimultaneously deforms and elongates the individual aluminum powderparticles causing an exposure of fresh new metal promoting the wettingof the surfaces thereof and their tenacious bonding to the backing strip4. The compacting and extrusion effect provided by the reduced rotationof the upper roll is best illustrated by FIGURE 2 which shows theformation of a buildup or wave 26 of the powder blend layer adjacent tothe inlet side of the upper roll 20 which is subsequently compacted andextruded into the dense compacted layer 24 as it passes between therolls. The reduced rolling rate of the upper roll 20 can be achieved byany one of a number of well known methods such als, for example, anindependent reduction drive mechanism or a slip clutch mechanismconnected to the upper roll. Depending upon the specific composition andproperties of the backing strip 4 employed, the hot rolling operationconcurrently produces a reduction in the thickness of the backing strip4 ranging up to about 5% of the original thickness. In addition todensifying, extruding, and bonding the backing strip and dense compactedlayer 24 together, the hot rolling operation also serves to accuratelysize the thickness of the composite strip as it leaves the rolls,

The composite strip 2S emerging from the exit side of the hot rollingoperation thereafter passes through a port in an intermediate partition30 into a cooling chamber 32 which is provided with a non-oxidizingatmosphere and chamber 32 must be maintained to achieve the rapid ocooling will, of course, vary depending upon related factors such as thesize and heat capacity of the composite strip, the length of the coolingchamber 32 and the linear speed of the composite strip therethrough.

Finally, the composite `strip 28 which has been cooled to about roomtemperature emerges through a port in an end partition 34 from thecooling chamber 32 and can be conveniently rolled on a take-up spool 36.In this form the resultant composite bearing strip can be fed throughconventional stamping and forming operations to produce bearings of thedesired configuration and size such as, for example, -sleeve typebearings and thrust washer bearings.

Analyses of the grain structure of the aluminum lead alloy based onphotomicrographs taken of hydrofluoric acid etched surfaces of thealloys produced at a magniiication of 500, revealed a relatively finedistribution of lead throughout the aluminum or aluminum alloy matrix.The phases of lead were somewhat oriented in the direction of rolling.

The tensile strength of the aluminum lead alloy and the bond strengthbetween the alloy surface layer and a steel backing strip are providedin the following table for four typical aluminum lead alloy compositionsmade in Sample Sample Sample Sample A B C D Properties:

Tensile Strength, psi-.. Bond. Strength (Shear),

In addition to the foregoing tensile and bond shear test data the-composite strip represented by samples A and B in the above table wereformed into conventional sleeve or shell type bearings of the typeemployed in automobile engines and were tested under actual operatingconditions. These tests substantiated the satisfactory operatingcharacteristics of the composite bearings under full load. In addition,the composite strip represented by sample B above was shaped in the formof thrust washers suitable for use in automotive transmissions and haveprovided excellent performance over a wide range of test conditionsexhibiting minimal wear, heat generation, and weight loss.

While it will be apparent that the preferred embodiments hereinillustrated are well `calculated to fulfill the objects above stated, itwill be appreciated that the invention is susceptible to modification,variation and change without departing from the proper scope or fairmeaning of the subjoined claims.

What is claimed is:

1. The method of making an aluminum lead alloy containing up to about70% lead of which up to about 5% thereof is in the form of lead monoxidecomprising the steps of providing a powder blend of aluminum and leadmonoxide powders, preheating the said powder blend at a temperatureranging from about 800 F. to about 1100 F. in a reducing atmosphereuntil substantially all of the lead monoxide is reduced to metalliclea-d, compacting the preheated said powder blend into a relativelydense mass, and thereafter cooling the said dense mass.

2. The method of making an aluminum lead alloy containing up to about70% lead of which up to about 5% thereof is in the form of lead monoxidecomprising the steps of blending an aluminum alloy powder consistingprimarily of aluminum with a lead monoxide powder in the proportionsranging up to about 72% lead monoxide powder and the balance aluminumpowder providing therewith a substantially homogeneous powder blend,preheating the said powder blend at a temperature ranging from about 800F. to about 1100 F. in a reducing atmosphere until at least about of thelead monoxide has been reduced to metallic lead, densifying thepreheated said powder blend under pressure into a relatively dense mass,and thereafter cooling the said dense mass in a non-oxidizingatmosphere.

3. The method of making an aluminum lead alloy containing up to about70% lead of which up to about 5% thereof is in the form of lead monoxidecomprising the steps of blending an aluminum alloy powder consistingprimarily of aluminum having a particle size less than mesh with a MillRun litharge powder in the proportions ranging up to about 72% lithargeand the balance aluminum alloy powder providing therewith asubstantially homogeneous powder blend, preheating the said powder blendat a temperature ranging from about 800 F. to about 1000" F. in areducing atmosphere until at least about 95% of the litharge has beenreduced to metallic lead, densifying the preheated said powder blendunder pressure into a relatively dense mass, and thereafter cooling thesaid dense mass in a non-oxidizing atmosphere.

4. The method of making a composite strip suitable for the manufactureof bearings and the like comprising the steps of providing a hard met-albacking strip and a substantially homogeneous powder blend of aluminumpowder and lead monoxide powder in the proportions of up to about 72%lead monoxide powder and the balance aluminum powder, superposing arelatively uniform layer of said powder blend on said backing strip,preheating said layer of said powder blend in a reducing atmosphere at atemperature ranging from about 800 F. to about ll F. for a period oftime sucient to substantially completely reduce said lead monoxide tometallic lead, densifying the preheated said layer on said backing stripby passing said strip and said layer thereon through a pair of rolls,one of said pairs of rolls in contact with said layer relating at aperipheral speed less than the linear speed of said layer causingconcurrent compacting and extrusion of said layer and tenaciouslybonding said layer to said backing strip, and thereafter rapidly coolingsaid composite strip in -a non-oxidizing atmosphere.

5. The method of making a composite strip suitable for the manufactureof bearings and the like comprising the steps of providing a hard metalbacking strip and a substantially homogeneous powder blend comprising analuminum alloy powder consisting primarily of aluminum and a leadmonoxide powder in the proportion of up to about 72% lead monoxidepowder and the balance aluminum powder, superposing a relatively uniformlayer of said powder blend on said backing strip, preheating said layerof said powder blend in a reducing atmosphere at a temperature rangingfrom about 800 F. to about ll00 F. for a period of time suflcient toreduce at least about 95% of said lead monoxide to metallic lead,densifying the preheated said layer on said backing strip by passingsaid strip and said layer thereon through a pair of rollers, the one ofsaid pair of rolls in contact with said layer rotating at a peripheralspeed less than the linear speed of said layer causing concurrentcompacting and o extrusion of said layer and a reduction of up to about5% in the thickness of said backing strip whereby said layer istenaciously bonded to said backing strip over substantially the entiresurface therebetween, and thereafter rapidly cooling said compositestrip in a non-oxidizing atmosphere.

6. The method of making a composite strip suitable for the manufactureof bearings and the like comprising the steps of providing a steelbacking strip and a substantially homogeneous powder blend comprising analuminum powder consisting primarily of aluminum and an alloying agentselected from the group consisting of silicon, copper, nickel, magnesiumand mixtures thereof and a Mill Run litharge powder in the proportionsof up to about 72% litharge and the balance aluminum alloy powder,superposing a relatively uniform layer of said powder blend on saidbacking strip, preheating said layer of said powder blend in a reducingatmosphere at a temperature ranging from about 800 F, to about 1000 F.for a period of time sufficient to reduce at least about of saidlitharge to metallic lead, densifying the preheated said layer on saidbacking strip by passing said strip and said layer thereon through apair of rolls, the one of said pair of rolls in conta-ct with said layerrotating at a peripheral speed ranging from about one-tenth to aboutone-fifth the linear speed of said layer causing concurrent compactingand extrusion of said layer and up to about a 5% reduction in thethickness of said backing strip whereby said layer and said backingstrip are tenaciously bonded together over substantially the entiresurface therebetween, and thereafter rapidly cooling said compositestrip in a non-oxidizing atmosphere.

References Cited by the Examiner UNITED STATES PATENTS 2,198,253 4/1940Koehring 29-149.5 2,749,604 6/1956 Latin 29-420.5 2,815,567 12/1957Gould et al. 29-l9l.2 X 3,104,135 9/1963 Morrison et al. 29-149.5 X

WHITMORE A. WILTZ, Primary Examiner.

THOMAS H. EAGER, Examiner.

1. THE METHOD OF MAKING AN ALUMINUM LEAD ALLOY CONTAINING UP TO ABOUT70% LEAD OF WHICH UP TO ABOUT 5% THEREOF IS IN THE FORM OF LEAD MONOXIDECOMPRISING THE STEPS OF PROVIDING A POWDER BLEND OF ALUMINUM AND LEADMONOXIDE POWDERS, PREHEATING THE SAID POWDER BLEND AT A TEMPERATURERANGING FROM ABOUT 800*F. TO ABOUT 1100*F. IN A REDUCING ATMOSPHEREUNTIL SUBSTANTIALLY ALL OF THE LEAD MONOXIDE IS REDUCED TO METALLICLEAD, COMPACTING THE PREHEATED SAID POWDER BLEND INTO A RELATIVELY DENSEMASS, AND THEREAFTER COOLING THE SAID DENSE MASS.
 4. THE METHOD OFMAKING A COMPOSITE STRIP SUITABLE FOR THE MANUFACTURE OF BEARINGS ANDTHE LIKE COMPRISING THE STEPS OF PROVIDING A HARD METAL BACKING STRIPAND A SUBSTANTIALLY HOMOGENEOUS POWDER BLEND OF ALUMINUM POWDER AND LEADMONOXIDE POWDER IN THE PROPORTIONS OF UP TO ABOUT 72% LEAD MONOXIDEPOWDER AND THE BALANCE ALUMINUM POWDER, SUPERPOSING A RELATIVELY UNIFORMLAYER OF SAID POWDER BLEND ON SAID BACKING STRIP, PREHEATING SAID LAYEROF SAID POWDER BLEND IN A REDUCING ATMOSPHERE AT A TEMPERATURE RANGINGFROM ABOUT 800*F. TO ABOUT 1100*F. FOR A PERIOD OF TIME SUFFICINT TOSUBSTANTIALLY COMPLETELY REDUCE SAID LEAD MONOXIDE TO METALLIC LEAD,DENSIFYING THE PREHEATED SAID LAYER ON SAID BACKING STRIP BY PASSINGSAID STRIP AND SAID LAYER THEREON THEREOF A PAIR OF ROLLS, ONE OF SAIDPAIRS OF ROLLS IN CONTACT WITH SAID LAYER RELATING AT A PERIPHERAL SPEEDLESS THAN THE LINEAR SPEED OF SAID LAYER CAUSING CONCURRENT COMPACTINGAND EXTRUSION OF SAID LAYER AND TENACIOUSLY BONDING SAID LAYER TO SAIDBACKING STRIP, AND THEREAFTER RAPIDLY COOLING SAID COMPOSITE STRIP IN ANON-OXIDIZING ATMOSPHERE.